So how does it work? Pure glucose (sugar) rates a 100 on the GI index and is the base against which all the other foods are measured. Other foods high on the index include ice cream and dried fruit, where foods low on the index include apples and beans.

Although diets tend to emphasize foods that are low on the GI, a food’s GI rating isn’t the only thing you need to consider. For example, brown rice actually ranks higher on the index than a Mars bar. Does this mean that a gooey convenience food will fit better into a healthy diet plan than fiber-filled grains? Dream on!

Remember that the glycemic index only measures the blood glucose response to a food. If the food is also high in fat and protein, it will have a lower GI rating but won’t necessarily be healthy. Because the candy bar contains fat (even though it’s the saturated, artery-clogging kind), the body’s insulin response is slower, placing the bar lower on the index than foods without fat, such as brown rice.

Confused?

Use this basic rule of thumb for following the glycemic index: Nutritious foods can be high on the index, so just pair them with another nutritious food that contains lean protein and healthy, unsaturated fats to give them a better GI rating. For example, if you’re having brown rice, drizzle some olive oil on a grilled chicken breast and eat that too.

Using the glycemic index as a guideline for healthy eating can help alleviate mood swings, fatigue, depression and energy crashes. So although it may be hard initially to swap that doughnut for an apple, your body will thank you in the end.